Knowledge of oxidative mechanisms in mammalian systems has advanced significantly in the past five years with significant implications into the fields of nutrition, physiology and toxicology. It has become evident that the relative contributions of mitochondria and peroxisones to long-chain fatty acid oxidation and themode of metabolic communication between these two organelles can affect several major metabolic processes. These include thermogenesis, ketogenesis, Beta-oxidation of long-chain fatty acids and indirectly amino acid and pyruvate oxidation. Therefore, directly or indirectly most all major energy yielding (ATP) processes can be affected. A connecting link between mitochondrial andperoxisomal fatty acid oxidation appears to be mediated be carnitine via short and medium-chain acylcarnitines. Mitochondrial andperoxisomal metabolism may be linked to thermal regulation, a secondary but important role of metabolism. Since some of the perosisomal oxidative processes are uncoupled, they may have considerable potential for heat generation. This may be particularly important in the relationship of brown fat tissue to thermogenesis. Two other important oxidative mechanisms will be discussed at the Food and Nutrition-Gordon Conference: lipid peroxidation and oxygenases and hydroxylases containing cytochrome P-450. Peroxidation of lipids reflects free radical events in polyunsaturated fatty acids which are associated with cell membranes. In addition to oxidative alteration of the structural lipids of the membrane , these free radical events may affect other cellular components causing irreverisble damage to cell structure, modification of function or cell death. Free radical mediated events can be triggered by reactive radicals produced by oxy genase and hydrolylase systems during the metabolism of zenobiotics. As a result of elevated oxygen tensions the role of free radical scvangers and other free radical quenching processes are very important. Diet and nutritional status have a very significant affect on lipid peroxidation reactions and it is the intent of these sessions to discuss these factors, how they are interrelated and the effect of nutritional status on these mechanisms.